1, physical method
Physical method of sewage treatment is the use of physical effects, separation of sewage in the main suspended state of pollutants, in the treatment process does not change the chemical properties of water.
(1) precipitation (gravity separation)
Sewage flow into the pool due to the reduced flow rate, sewage solids in the neutral effect of precipitation, so that the solids and water separation.
This process separation effect is good, simple and easy to implement, widely used, such as sewage treatment plant sand sedimentation tank and sedimentation tank. Sand sedimentation tank is mainly to remove the sewage density of solid particles, sedimentation tank is mainly used to remove a large number of sewage in the form of particles of suspended solids.
(2) screening (interception)
Use of screening media to intercept the suspended matter in the sewage. Belonging to the sand filtration treatment equipment are grills, microfilters, sand filter tanks, vacuum filters, filter presses (the latter two are mainly used for sludge dewatering) and so on.
(3) air flotation (floating)
For some fine particles whose relative density is close to that of water, it is difficult to sink or float in the water due to its self-weight, and air flotation devices can be used. This method of air into the sewage, and make the situation of tiny bubbles from the water precipitation, sewage density close to the water of tiny particles of pollution impurities (such as emulsified oil) adhering to the bubbles, and with the bubbles to the surface of the water, the formation of foam slag and remove. According to the different ways of air intake, air flotation equipment has pressurized dissolved vapor flotation method, impeller air flotation method and jet air flotation method. In order to improve the effect of air flotation, it is sometimes necessary to add coagulants to the sewage.
(4) centrifugal and cyclone separation
Suspended solids or emulsified oil containing sewage, suspended solids and wastewater due to the quality of different, by the centrifugal force is also different, the quality of the suspended solids are thrown to the outside of the sewage, so that suspended solids and sewage through their respective outlets out of the equipment, so that the sewage can be purified.
2. Chemical method
The chemical treatment of sewage is to add chemicals to the sewage, the use of chemical reactions to separate and recycle pollutants in the sewage, or its conversion into harmless substances. There are several types of chemical treatment methods.
(1) coagulation method
Coagulation method is to the sewage is added to a certain amount of chemicals, after destabilization, bridging and other reaction processes, so that the pollutants in the sewage cohesion and sedimentation. The colloidal state of the pollutants in the water is usually negatively charged, colloidal particles repel each other to form a stable mixture, if the water with the opposite charge of the electrolyte (coagulant) can make the colloidal particles in the sewage is electrically neutral, and in the molecular gravitational force, cohesion into large particles sinking.
(2) neutralization method
The process of chemically eliminating excess acid and alkali in sewage so that its pH value reaches about neutral is called the neutralization method. Treatment of acid-containing sewage with alkali as a neutralizing agent, treatment of alkaline-containing sewage with acid as a neutralizing agent, can also be blown into the flue gas containing CO2 for neutralization. Acid and alkali refers to inorganic acid and inorganic alkali, generally in accordance with the "waste to waste" principle, can also be used to neutralize the treatment of pharmaceuticals, can be continuous, can also be intermittent.
(3) redox method
Sewage in the dissolved state of organic and inorganic substances, in the addition of oxidizing and reducing agents, due to the migration of electrons and oxidation and reduction to form harmless substances. Commonly used oxidizing agents are oxygen in the air, pure oxygen, bleaching powder, ozone, chlorine, etc. The oxidation method is mostly used to treat cyanide-containing phenol wastewater. Commonly used reducing agents are iron filings, ferrous sulfate, sodium bisulfite, etc. The reduction method is mostly used to treat chromium-containing and mercury-containing wastewater.
(4) Electrolysis
In the wastewater inserted into the electrode and through the current, then in the cathode plate to receive electrons. During the electrolysis of water, oxygen is produced on the anode and hydrogen is produced on the cathode. The above combined process causes oxidation to occur on the anode and reduction to occur on the cathode. At present, electrolysis is mainly used to treat chromium-containing and cyanide-containing wastewater.
(5) adsorption method
Sewage adsorption treatment is mainly the use of solid material surface adsorption of pollutants in the sewage, adsorption can be divided into physical adsorption and biological adsorption and so on. Physical adsorption is between the adsorbent and adsorbent under the action of molecular force, does not produce chemical changes, and chemical adsorption law so that the adsorbent and adsorbent under the action of chemical bonding force adsorption, so the chemical adsorption of selective stronger. In addition, biosorption can also occur under biological action. The adsorbents commonly used in wastewater treatment are activated carbon, sulfonated coal, diatomaceous earth, coke and so on.
(6) chemical precipitation method
Add some chemicals to the sewage, so that it reacts with certain dissolved substances to produce insoluble salts to precipitate down. Mostly used in the treatment of industrial wastewater containing heavy metal ions.
(7) ion exchange method
Ion exchange method is widely used in sewage treatment. The ion exchange agent used is divided into inorganic ion exchange (natural zeolite and synthetic zeolite), organic ion exchange resin (strong acidic cation resin, weak acidic cation resin, strong alkaline anion resin, weak alkaline anion resin, ao and resin, etc.). When treating wastewater by the ion exchange method, the selectivity of the resin must be considered. The exchange capacity of the resin for various ions is different, which mainly depends on the size of the affinity of each ion for the resin, also known as the size of the selectivity, but also take into account the regeneration method of the resin.
(8) Membrane Separation Method
Dialysis, electrodialysis, ultrafiltration, microfiltration, reverse osmosis, etc. through a special semi-permeable membrane separation of ions and molecules in the water, collectively referred to as membrane separation method. Electrodialysis is mainly used for water desalination, recovery of certain metal ions. Reverse osmosis is mainly the role of the membrane surface chemical nature of the role he separates the solute particle size, high rate of desalination, the required working pressure; ultrafiltration and reverse osmosis and the same material, but ultrafiltration is the role of sieve filtration, the separation of solutes Particle size is large, high permeability, desalination rate is low, the working pressure is small.
3, biological method
The biofilm method of sewage is to take certain artificial measures to create an environment conducive to microbial growth and reproduction, so that microbial proliferation, in order to improve the microbial oxidation, decomposition of organic pollutants are degraded and converted into harmless substances, so that the sewage can be purified.
Biological treatment method can be divided into aerobic treatment method and anaerobic treatment method two categories. The former treatment efficiency, good results, widely used, is the main method of biological treatment. The processes belonging to the biological treatment method are as follows.
(1) activated sludge method
is the most widely used biological treatment technology. Air continuously drummed into the sewage containing a large number of dissolved organic pollutants, after a period of time, the water both the formation of a large number of aerobic microorganisms breeding floc - activated sludge,
Activated sludge can be adsorbed in the water of organic matter, sewage in the microorganisms in the activated sludge in the organic matter as food, energy, and constantly grow proliferate, organic matter is decomposed, removed, so that the sewage can be purified. Decomposition, removal, so that sewage can be purified. Generally, the effluent treated by the aeration tank is a sewage-mixed liquid containing a large amount of activated sludge, and the water is purified and discharged through sedimentation and separation, and the sludge after sedimentation and separation is used as seed sludge, and part of it flows back to the aeration tank. Activated sludge method since its emergence, after more than 80 years of evolution, there are various
variations of the activated sludge method, but the principle and process have not fundamentally changed.
(2) Common activated sludge method
This method has been widely used and is a common process in many sewage treatment plants. Traditional activated sludge method is the sewage and return sludge from the first section of the aeration tank is introduced, is a push flow to the end of the aeration tank outflow, this method is suitable for the treatment of sewage with high requirements, water quality is more stable, but the adaptability of the change of the load is weaker, and later on this basis has produced some improved form.
(3) multi-point water intake method
In order to make the organic load in the tank close to a certain value, the sewage from several points of separate inflow, is conducive to solving the problem of overload.
(4) adsorption and regeneration method
Contact tank activated activated sludge adsorption of pollutants, sludge and water separation, the adsorption of pollutants in the aeration tank for oxidation. This method is conducive to increase the sewage treatment capacity, there is a certain resistance to shock load capacity.
(5) delayed aeration method
The sewage in the aeration tank to extend the aeration time, is conducive to the complete oxidation, the amount of sludge is small, the method is suitable for small sewage treatment plant.
(6) anaerobic-anoxic
- aerobic activated sludge method In the conventional activated sludge method for the removal of organic pollutants at the same time, in order to be able to effectively remove nutrients such as nitrogen and phosphorus, people put the combination of anaerobic, anoxic, aerobic conditions to the activated sludge method, so that the anaerobic-anoxic- aerobic conditions in the reaction aeration tank at the same time or repeated cycles to realize the formation of anaerobic-anoxic- aerobic Activated sludge method. There are also processes that use the anaerobic- aerobic activated sludge method.
(7) intermittent activated sludge method
The sewage flows into a single reaction tank, according to time through the program to control the process. In a working cycle of the reaction tank, the operation program in order for the water inlet, reaction, sedimentation, water and standby processes. The method is suitable for small and medium-sized water and water quality of the occasion, in favor of automated control; through the adjustment of the operation, the method can also be dephosphorized denitrogenation and chemical treatment, in favor of sewage reuse.